Probing the in-Medium QCD Force by Open Heavy-Flavor Observables

TL;DR

This paper investigates the in-medium QCD force by calculating heavy-quark transport properties using a T-matrix approach, and compares the resulting heavy-flavor observables with experimental data to understand the strength of the interaction in the quark-gluon plasma.

Contribution

It introduces a T-matrix formalism with off-shell effects to compute charm-quark transport coefficients based on lattice-QCD data, and assesses their impact on heavy-flavor observables in heavy-ion collisions.

Findings

Strongly-coupled T-matrix yields elliptic flow similar to internal energy potential.

Weakly-coupled T-matrix results in lower elliptic flow than observed.

Long-range confining force influences heavy-quark dynamics at low momentum.

Abstract

The determination of the color force in a quark-gluon plasma (QGP) is a key objective in the investigation of strong-interaction matter. Open and hidden heavy-flavor observables in heavy-ion collisions (HICs) are believed to provide insights into this problem by comparing calculations of heavy-quark (HQ) and quarkonium transport with pertinent experimental data. In this work, we utilize the $T$-matrix formalism to compute charm-quark transport coefficients for various input potentials previously extracted from simultaneous fits to lattice-QCD data for HQ free energies, quarkonium correlators and the QGP equation of state. We investigate the impact of off-shell effects (spectral functions) in the QGP medium on the HQ transport, and compare to earlier results using the free or internal HQ energies as potential proxies. We then employ the transport coefficients in relativistic Langevin simulations for HICs to test the sensitivity of heavy-flavor observables to the HQ interactions in the QGP. We find that a strongly-coupled $T$-matrix solution generates a HQ elliptic flow comparable to the results from the internal energy at low momentum, driven by a long-range remnant of the confining force, while falling off stronger with increasing 3-momentum. The weakly coupled $T$-matrix solution, whose underlying potential is close to the free energy, leads to an elliptic flow well below the experimentally observed range.